This invention relates to liquid polysulfides and sealants made therefrom whose moisture Vapor transmission rates are extremely low. More particularly, it relates to liquid polysulfides made from mixtures of an alkylene dihalide and a chloroethyl formal.
Oligomeric polysulfides based on bis-(2-chloroethyl formal) have been available commercially for over 30 years. These polymers are made in two steps, the first of which is a dispersion polymerization of the formal with sodium polysulfide in water. In the second step, the high molecular weight (about 100,000) polymer is reductively cleaved with sodium hydrosulfide and sodium sulfite to a material whose sulfide linkages are essentially all disulfide linkages. The product, a liquid oligomeric dimercaptan having a molecular weight of 1000-7000, may be cured with a metal oxide to form coatings and sealants. These conventional formal-based sealants suffer from relatively high moisture vapor transmission rates compared to butyl-based sealants and polyurethane sealants.